The prior art sometimes places the gold overlaying conductors directly adjacent to the nickel-chromium resistor material. During metal film deposition and subsequent heat treatments to stabilize the resistors, a destructive inter-diffusion takes place between the nickel-chromium (ni-chrome) alloy and the gold conductor. The chromium diffuses into gold at a much more rapid rate than the gold goes into the chromium, creating voids in the resistor film which result in intermittent and ultimately open circuits.
Other prior art methods use nickel as a diffusion barrier layer between the gold conductor and the nickel-chromium alloy resistor. This type barrier serves only to delay the process, but does not act as a corrective measure.
Further, the etching process to open up the resistors presents a control problem since the etching chemicals used to remove the nickel barrier also attack the nickel in the ni-chrome resistor, altering both the established value and the temperature characteristics.